Growth factors are substances, including peptides, which affect the growth and differentiation of defined cell populations in vivo or in vitro. Normal bone formation occurs during development, bone remodeling occurs in adult life, and bone repair occurs in order to preserve the integrity of the skeleton. Bone formation, remodeling and repair involve bone resorption by osteoclasts and bone formation by osteoblasts. Cell differentiation and the activity of osteoblasts and osteoclasts are regulated by growth factors. Thus, any interference between the balance in cell differentiation and resorption can affect bone homeostasis, bone formation and repair.
Osteoblasts are derived from a pool of marrow stromal cells (also known as mesenchymal stem cells). MSC are present in a variety of tissues and are prevalent in bone marrow stroma. MSC are pluripotent and can differentiate into chondrogenic or osteogenic cells including osteoblasts, chondrocytes, fibroblasts, myocytes, and adipocytes.
The induction of ectopic bone formation by demineralized bone matrix (DBM) has been described. (Urist, M. R.: Bone: Formation by autoinduction. Science 150:893-899, 1965; Urist, et al., Purification of bovine morphogenetic protein by hydroxyapatite chromatography. Proc. Natl. Acad. Sci. USA 81:371-375, 1984; Urist, M. R. Emerging concepts of bone morphogenetic protein. In Fundamentals of Bone Growth: Methodology and Applications, Boston C.R.C. Press, pp. 189-198, 1991.) Further, the properties of the partially purified protein fraction, bone morphogenic protein/non-collagenous protein (“BMP/NCP” or “BMP”s) have been described. (Urist, et al. Methods of Preparation and Bioassay of Bone Morphogenetic Protein and Polypeptide Fragments. In Methods in Enzymology. Vol. 146. New York, Academic Press, pp. 294-312, 1987; Urist, et al., Hydroxyapatite affinity, electroelution, and radioimmunoassay for identification of human and bovine bone morphogenetic proteins and polypeptides. In Development and Diseases of Cartilage and Bone Matrix. New York, Alan R, Liss, Inc., pp. 149-176, 1987.)
BMP/NCP was never purified to homogeneity, but other investigators have used similar starting materials to clone a number of recombinant “BMPs.” However several of these molecules have little or no osteogenic activity. “BMPs” and other osteogenic factors have been studied for use in clinical applications. However, the cost of using minimally effective dosages of BMP-7, for example has been a limiting factor in clinical use. Therefore, effective and affordable compositions and methods are desired for clinical applications relating to bone.